Preliminary Study on The Damage Effect of 297 nm Narrow-band LED Irradiation at Extremely Low Light Intensity of Microwatt on The Cornea of Infancy Rabbits
Objective To investigate the damage threshold and pathological characteristics of cornea of infancy rabbits irradiated by 297 nm narrow-band LED at extremely low light intensity of microwatt.Methods The subjects of the study were 7 Chinese black rabbits with 14 eyes,irradiated by a narrow-band LED light source with a wavelength of(297±5)nm.According to different power densities,the rabbits were divided into 3 groups:5 μW/cm2 group(Group A),10 μW/cm2 group(group B),15 μW/cm2 group(group C),and according to different energy density,each power density group was further divided into 4 subgroups:18 mJ/cm2 group(A1,B1,C1),24 mJ/cm2 group(A2,B2,C2),30 mJ/cm2 group(A3,B3,C3),36 mJ/cm2 group(A4,B4,C4).There were 2 eyes in the control group and 1 eye in each experimental group.Corneal turbidity was observed with slit lamp every 6 h after irradiation,and the site,area and depth of corneal damage were evaluated and recorded by fluorescein sodium staining 24 h after irradiation,which were the basis for determining the damage threshold.HE staining was performed to evaluate the pathological changes of corneal tissues.Results The damage thresholds of 297 nm narrow-band LED irradiation at power densities of 5,10 and 15μW/cm2were 30,24 and 18 mJ/cm2,respectively.The results of sodium fluorescein staining showed that punctate and flaky staining appeared in the corneal pupil area 24 h after exposure to the doses above the damage threshold and damage threshold.HE staining showed that corneal epithelial cells were sparsely distributed and disordered,and basal layer cells were swollen and vacuolated.The arrangement of superficial stromal collagen fibers was loose and the void increased,indicating stromal edema.No damage was found in other cornea layers and lens.Conclusions The approximate damage thresholds of cornea of 297 nm narrow-band LED irradiation at power densities of 5,10 and 15 μW/cm2 were 30,24 and 18 mJ/cm2,respectively.The lower the power density,the higher the damage threshold,and the damage sites were mainly corneal epithelium and stroma layer.
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